The second element on which global connectivity depends is connection redundancy, which takes into account the relevance of a layer in the all-layers zone's connectivity. This quantity measures to what extent the removal of the links belonging to a specific layer affects the capacity to reach a neighbouring zone from the considered one. Redundancy in general is a measure of the strength of node-node connections considering the links connecting the two nodes over all the layers of the network. Before defining the connection redundancy, however, we need to introduce the layer \(l\)  relevance, \(LR(u,l)\) , for the node \(u\) .
\(LR(u,l)\)  can be defined as the ratio between the number of nodes that disconnect from node \(u\)  if all the links of layer \(l\)  are removed (which is the same as removing an entire layer to the multiplex network) and the number of nodes reachable before the removal of the layer[1]}:
